Every day, it goes through a stunning number of invisible functions and processes in an effort to keep you functioning at optimal levels. These activities are governed not only by a "master clock" located inside the hypothalamus portion of our brains, but by trillions of other clocks living inside the cells of our body. Together, these clocks work to keep our "circadian rhythms"—defined as "physical, mental and behavioral changes that follow a daily cycle"—in sync. Keeping these internal clocks calibrated is key to your health and well-being. They're complex, and their effects are wide-ranging. But we do know there are some common behaviors that throw these internal clocks out of whack, rendering them less effective at doing their No. 1 job—making you the healthiest human being possible.

1. You Think Bedtimes Are Only for Children

On a typical weekday, you usually hit the hay anywhere between 10:30 p.m. and 12:30 a.m.
But after a particularly exhausting day, you may pass out much earlier. Other nights, you might party into the wee hours of the morning. If this sounds like you, you're not alone. Millions of Americans struggle to establish a consistent bedtime, and it's making us tired, dumber and less healthy.

Here's the thing—even if you're totaling roughly the same number of hours of sleep each night, when you go to bed remains a critical factor. A recent study published in the journal Scientific Reports looked at the relation between irregular sleep schedules and academic performance in university students. Despite the fact there was no significant difference in the average daily sleep duration between participants with irregular bedtimes and participants with regular bedtimes, irregular bedtimes were associated with lower grade point averages.

Having no regular bedtime wreaks havoc on your biological clocks, affecting its ability to regulate those aforementioned invisible functions. For example, melatonin—an important brain hormone that helps regulate sleep—was released nearly three hours later in the students with irregular bedtimes than it was in the students with a regular bedtime. So for the students with irregular bedtimes, they might've been sitting in their 9 a.m. class the next morning, but there bodies were actually operating like it was 6 a.m. We're naturally more alert at 9 a.m. than we are at 6 a.m., so that's a huge issue.

It's believed that disrupting our circadian rhythms can have a negative effect on our gut bacteria, which in turn can have far-reaching health effects all throughout the body. While it's also important to establish a consistent wake-up time, that should come fairly naturally once you manage to nail down a consistent bedtime.

2. You "Save" Your Calories for Nighttime

You skip breakfast, or opt for something small—say a single piece of fruit. Then you don't eat again until you consume a small salad for lunch. Then you don't eat again until dinner, where, feeling confident that you've starved yourself all day, you gorge. Then you help yourself to dessert, then a snack, and then another, and so on until you finally fall asleep. Millions of Americans follow a similar eating schedule every single day. While they might hit their calorie target, they're constantly hungry, consistently cranky and not seeing positive changes in their body.

As it turns out, "saving" the majority of your calories for the evening/nighttime doesn't jive well with your circadian rhythms. When it gets dark out, the master clock in your brain signals to the rest of your body that it's time to prepare for rest. But then when you binge on snacks all night, the clocks throughout your body—such as in organs like the pancreas—must spring into action.

"The pancreas is listening to signals related to food intake. But that's out of sync with what the brain is telling it to do," Fred Turek, Director at Northwestern University's Center for Sleep & Circadian Biology, told NPR. "So if we're sending signals to those organs at the wrong time of day—such as eating at the wrong time of day—[we're] upsetting the balance." An increasing amount of research is finding that our bodies react more positively to eating most of our calories early in the day as opposed to later.

A 2013 study published in the journal Obesity was conducted with two groups of similarly obese and overweight women over a 12-week period. Both groups were put on a strict, 1,400-calorie-a-day diet that consisted of foods like grilled chicken, melon, egg whites, turkey breast, green salad and milk chocolate. One group ate a breakfast of 700 calories, a lunch of 500 calories and a dinner of 200 calories. The other ate a breakfast of 200 calories, a lunch of 500 calories and a dinner of 700 calories.

After the 12-week period, the group that ate the large breakfast and small dinner had lost nearly 2.5 times as much weight as the group that ate the small breakfast and large dinner. The big-breakfast group lost approximately 18 pounds, compared to 7 pounds lost by the large-dinner group. Remember, the two groups ate the exact same number of calories and the exact same foods every day—just in a different order. The big-breakfast group also reported feeling less hungry throughout the day.

"An isocaloric weight loss diet with exchanged caloric intake between breakfast and dinner differentially influences weight loss, waist circumference, serum ghrelin and lipids, appetite scores, and insulin resistance indices in overweight and obese women with the metabolic syndrome," the study's authors concluded. If you want to eat more in-tune with your internal clocks, aim to eat more of your calories earlier in the day.

3. You're Bathed in Blue Light 24/7

It's estimated that the first modern humans came into existence 200,000 years ago. Indoor lighting became commonplace about 120 years ago. The first iPhone was released 10 years ago.

Our bodies haven't exactly had much time to adapt to a world that's become bathed in artificial light. 99 percent of people living in the continental U.S. and Western Europe don't experience "true night," a phrase for the level of natural darkness that can only be achieved in absence of the glow of artificial lights. Inside our homes, the sources of artificial light are more numerous than ever—not just lamps and televisions, but smartphones, tablets, laptops, etc. Our body relies largely on natural light to keep our circadian rhythms synchronized, but it has trouble discerning between artificial light and sunlight. Nowadays, much of the artificial light doing this harm can be categorized as "blue light." Part of the visible light spectrum and defined as having a wavelength between 450-495nm, blue light is emitted from many digital devices; such as computers, smartphones and televisions. A recent study published in the journal Ophthalmic & Physiological Optics looked at just how damaging this blue light can be. From ScienceDaily:

Study participants, ages 17-42, wore short wavelength-blocking glasses three hours before bedtime for two weeks, while still performing their nightly digital routine. Results showed about a 58 percent increase in their nighttime melatonin levels, the chemical that signals your body that it's time to sleep. Those levels are even higher than increases from over-the-counter melatonin supplements.

While there's still more research to be done on the harmful effects of blue light on sleep and circadian rhythms, the existing evidence paints a grim picture. "Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity," writes the Harvard Health Letter.

So not only is exposure to blue light at night making you groggier in the short term, but it could also be slowly killing you. To combat this issue, you can start by avoiding bright screens during the two hour lead-up to sleep. If you really can't give up your iPhone before bed, we recommend using "Night Shift" mode. There are also affordable blue light-blocking glasses available for purchase, similar to what was used in the aforementioned study.

Brandon Hall
- Brandon Hall is an Assistant Content Director for STACK. He graduated from Lafayette College, where he played football and graduated with a Bachelor's degree in English.
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